Image recording apparatuses for recording color images onto recording media using an inkjet system by moving an ejection part relative to the recording media have conventionally been used, the ejection part including a plurality of nozzles each ejecting fine droplets of ink. Color images are recorded by forming ink dots at each pixel position on a recording medium on the basis of halftone image data generated through halftone processing. Such image recording apparatuses, however, may cause poor color reproduction due to colors becoming dull or cockling (phenomenon where the surface of a recording medium becomes rippled) as a result of dots of multiple color inks greatly overlapping at each pixel position on a recording medium.
Meanwhile, Japanese Patent Application Laid-Open Nos. 11-010918 (Document 1) and 2000-354172 (Document 2) disclose methods for reducing graininess of images by recording only a dot of a single color at each pixel position. In Japanese Patent Application Laid-Open No. 2010-241052 (Document 3), halftone processing is performed on a color image on the basis of an evaluation index that indicates the degree of dispersion of the overlapping of dots on a recording medium. Through this, it is possible to suppress the overlapping of dots and reduce graininess of images.
Although Documents 1 and 2 can suppress dulling of color due to overlapping of multiple color dots, it becomes difficult to represent dark mixed colors. In addition, if ink landing positions shift from their desired positions and change the overlapping state of multiple color dots, the influence of that change is greatly reflected in coloration. Document 3 can also suppress dulling of color due to overlapping of multiple color dots, but it gives no consideration to the total amount of ink applied to each pixel position. It is thus difficult to appropriately suppress cockling.